In my U.S. Pat. No. 3,831,065 issued Aug. 20, 1974 and entitled ELECTRONIC PUSH BUTTON COMBINATION LOCK, there is disclosed a push button keyboard and associated circuit for installation in commercial establishments such as hotels, motels and the like. The locks as described in this United States Patent are wired to a central desk or office in the hotel or motel at which point various different combinations can be programmed into the locks by the hotel desk manager or other personnel thereby providing an assigned room a combination which may be selected by the customer. A primary purpose of such a system is to avoid the problem associated with lost hotel and motel keys.
The circuit claimed and disclosed in my prior above identified United States Patent utilizes a ring counter having a number of stages one greater than the number of coded digits so that successive comparison of the keyboard input code can be made with the stored codes, the one extra or last stage providing an unlocking signal.
While the foregoing circuit works well for its particular application in hotels and motels and includes the very important feature of permitting a combination to be programmed into any particular locking circuit for any particular room from a central office location, it is not well suited for apartments or residential use. In this respect, a primary difficulty resides in the necessity of wired connections to the lock to provide the necessary energy for electrically throwing the locking bolt. Batteries, of course, could be used but their energy would be drained relatively quickly following several unlocking and locking operations. Also, since wiring must be used to connect the locks to the central office, thus necessitating expensive installation operations in any event, there is no need to use battery power in my foregoing system.
In the case of providing push button electronic combination locks for apartments or residences, various problems arise. First, such a lock must be capable of simple and inexpensive installation with minimum alterations to the premises. This requirement itself forecloses the use of any type of electronic push button combination lock which requires wiring to remote electrical power sources or even around marginal portions of the door or door frame itself. Second, any push button or electronic combination lock for use in apartments or residences should desirably have the capability of storing more than one combination so that, for example, in the case of an apartment complex a landlord will have access to all of the apartments by means of a master combination different from the individual tenant's various combinations. Moreover, the tenant of a specific apartment may wish to provide access to another person such as a maid without the maid knowing the tenant's specific combination. In this respect, the lock involved should desirably incorporate circuitry permitting either or both the landlord and tenant to alter or disable the combination of the tenant and maid respectively.
Finally, the electronic lock should be capable of operating with combinations of digits made up by the user ranging from one or more digits. In other words, a lock which is not restricted to the total number of digits making up the combination code would be far more versatile.